Think back to when you were in a maths classroom, and the teacher set a difficult problem. Which of the two following responses is closer to the way you reacted?

A: Oh no, this is too hard for me. I’m not even going to seriously try and work it out.

B: Ah, this is quite tricky, but I like to push myself. Even if I don’t get the answer right, maybe I’ll learn something in the attempt.

Early in her career, the psychologist Carol Dweck of Stanford University gave a group of ten-year-olds problems that were slightly too hard for them. One group reacted positively and loved the challenge. She says they had a ‘growth mindset’ and are focused on what they can achieve in the future. But another group of children felt that their intelligence was being judged and they had failed. They had a ‘fixed mindset’ and were unable to imagine improving. Some of them looked for someone who had done worse than them to boost their self-esteem.

Professor Dweck believes that there is a problem in education at the moment. For years, children have been praised for their intelligence or talent, but this makes them vulnerable (脆弱的) to failure. They become performance-oriented, wanting to please by getting high grades, but they are not interested in learning for its own sake. The solution, according to Dweck, is to lead them to become mastery-oriented (i.e., interested in getting better at something). She claims that the ever-lasting effort over time is the key to outstanding achievement.

Psychologists have been testing these theories. Underperforming school children on a Native American reservation were exposed to growth mindset techniques for a year. The results were nothing less than incredible. They came top in regional tests, beating children from much more privileged backgrounds. These children had previously felt that making an effort was a sign of stupidity, but they came to see it as the key to learning.

HOW BIG should a business team be?It is an enormously important issue for companies, Teams that are too small may lack the skills required to get the job done:teams that are too big may be impossible to co-ordinate.

Robin Dunbar.an anthropologist at Oxford University,has done a lot of work on primate(灵长目）groups.His argument is that the size of the group is linked to the size of the brain.With their large brains,humans can cope with larger bands,A larger social group has many advantages,allowing for greater protection and specialization.

Whereas 150 is sometimes referred to as the"Dunbar number",the academic himself in fact refers to a range of figures.He observes that humans tend to have five intimate friends,15 or so good friends,around 50 social friends and 150-odd acquaintances.

Running a larger network can be difficult.The armed forces have spent more than 1,000 years experimenting with unit size.A Roman centurion(百天长）oversaw 100.The modern American army company has 180 members.Britain's equivalent numbers 120.These are rough estimates,rather than fixed figures.But it is striking that many group activities seem to be close to a Dunbar number. The Special Air Service of Britain has four-man patrols;when your life depends on it,you need to have absolute trust in your colleagues.As a result,such groups are limited in size.

For much of economic history,work was conducted in small units by peasants,tenant farmers and craftsmen.The coming of powered machinery enabled production at a much larger scale,with workers crowded into factories.These days the rise of the service economy means that workers are no longer concentrated in such large groups.

This may not be a bad thing.It was easy for employees in large factories to regard remote company owners as "them"rather than"us".The modern company may settle on a model with a small group of"core"workers and a larger group of contract workers.The result may be more united within the core staff but the non-core staff may be less well treated.The small core teams may work effectively.The big question will be the effect on morale of those outside those teams.

Aspirin has long been believed to help prevent heart attacks and strokes(中风).Some studies have shown that it also has a protective effect against certain types of cancer. As a result, some people religiously pop a low-dose(低剂量的) aspirin after breakfast every day (never take one on an empty stomach). But now its status as a wonder drug has come into question, following a meta-analysis of trial evidence.

A meta-analysis reviews the results of a large number of trials and can therefore come to more certain conclusions. This latest review was published this May in The Journal of the American Medical Association.It focused on the connection between aspirin use and cardiovascular(心血管的) and bleeding events. It found that the well-known risk that aspirin can cause internal bleeding is as great as the benefits of preventing heart attacks and strokes. In some cases, the risk even outweighs the benefits.

Aspirin thins the blood, thus helping to prevent blood clots (血栓). For his reason, it is a good drug for protecting people who have already had a heart attack or stroke from having another. However, the 164,225 people in these trials had no history of cardiovascular disease. They were monitored for an average of six years, during which time they took a daily aspirin or placebo(安慰剂).Among those who took aspirin, there were about 11% fewer heart attacks and strokes but 43% higher likelihood of a major bleeding episode in the stomach, brain or intestine(肠道).

Dr Sean Zheng, a cardiology(心脏病学) researcher at King’s College London, said that taking a daily aspirin couldn’t be recommended for healthy people. But there might still be a case for people with a higher risk of a heart attack or stroke, he added. However, it would be important to consider the bleeding risk.

“Aspirin use requires discussion between the patient and their physician, with the knowledge that any small potential cardiovascular benefits are weighed up against the real risk of severe bleeding." he said.

The findings reflect the average likelihood of bleeds or heart attacks among the patients in all the trials. There will be people among them who would be better off taking aspirin and those who will be worse. It's yet another situation where we need to weigh up our individual risk and benefit--- maybe with the help of an understanding GP.