And we were all going to have to learn Japanese because they worked harder, saved more, produced cars which didn't fall apart and were getting the better of their European and American counterparts in virtually every market. With this background, you won't be surprised to learn that I am sceptical about heavily- marketed investments that are based on confident assumptions about the long term. My experience suggests that if these assertions do come true, it can be as much down to chance as to superior insight. Moreover, the accuracy of an economic forecast does not guarantee the consistent success of investment decisions based upon it. It may well be that we are living in a commodity super-cycle, where raw material prices keep on rising for a long time; it may well be that in our working lives China will overtake America in economic terms. The problem is, these judgments do not provide a clear sign at any given point which investments to buy and which to sell. They are, even if correct, only small, intermediate steps in a much longer process of analysis and discussion. Moreover, the "expert" views that get most attention are not necessarily those which are right. In fact, the opposite is more likely to be true. Academic studies confirm that "complex and cautious trumps simple and confident": in other words pundits who hammer away at a core theoretical theme are consistently less reliable than those who are more doubtful, more hesitant, and who explore a wider range of possibilities. Now, just ask yourself, who is likely to get more attention, either in the investment world or in general: the diffident, wary introvert or the table-thumping extrovert? On that basis I would like to propose Howlett's Paradox: "In order to be a successful long-term investor, you need to be a flexible, pragmatic opportunist." That doesn't necessarily mean you go to the other extreme and chase every passing fad, flailing wildly around at a succession of unco-ordinated "themes", most of which bear the clear imprint of a plausible brokers' story about the latest "hot" market. There is a middle course which, by concentrating on things about which we can be reasonably confident, points investors towards sectors where the wind is at our backs rather than in our faces. The first such sector is healthcare. Problems with downward pricing pressure from governments and health insurers are real, but my guess is that the sector worldwide will see sales growth better than that of the economy in general.The reason is that we are getting older, sicker, richer and smarter: more people are living to an age at which they are increasingly vulnerable to ill health; however, as we become gradually richer and as scientists find more and more ways to treat us, there are increased resources to deal with the problem - and more opportunities to make a decent return. The second is agriculture. The world has about five billion hectares of farmed land, which needs to feed seven billion people - that's about a football pitch for each of us. The total farmed area is gradually shrinking while the population continues to grow and, as a result, there is steadily increasing pressure for greater efficiency and productivity at every link in the food chain - "from farm to fork". Companies that are on the right side of these trends are in a position to deliver great returns to shareholders. The third is energy. Oil may not be about to run out, but even the optimists admit that it is getting harder to find and more expensive to extract. This makes attractive investments out of oil companies that have solid reserves and a good exploration record; it also helps service companies with clear technical expertise; and it creates an ideal environment for companies in renewable and alternative energy. Being in these sectors does not guarantee success and investors will want to cast their nets more widely, but at least you should cast where there are lots of fish. • Gareth Howlett is fund manager director at Brooks Macdonald Asset Management