Ask most investors what would help them most and plenty would say a reliable view of what markets are about to do. It's an understandable answer, but nobody can supply it, and the search for it tends to pull attention away from the part of investing people do control, which is how they behave.
Why forecasts fall short
Every year brings a fresh batch of predictions about growth, interest rates, currencies and where the indices will finish. Some turn out to be right, as you'd expect when enough people make enough guesses. Far fewer are right year after year. Markets react to events nobody saw coming and then to everyone else's reaction, which is hard to call in advance, even for people who know the economics well. Professionals with full-time teams and the best data often disagree with one another, which says something about how uncertain the exercise is. A correct forecast tells you little about whether the next one will be.
The bigger issue is what a forecast does to a portfolio once it's built in. If the view is wrong, the portfolio is exposed to something it wasn't designed for, and the cost is real money.
How emotion affects returns
When markets fall, selling starts to look sensible. When they rise, buying whatever has done best lately looks just as sensible. Both feel reasonable at the time, but together they can leave someone selling after prices have dropped and buying after they've climbed, which is close to the opposite of what they intended.
A fall only becomes a loss once the investment is sold, so selling out of fear can turn a temporary setback into a permanent one. Recoveries tend to start while the news is still poor, and an investor waiting to feel comfortable again may arrive after a good part of the rebound has gone.
Almost everyone finds a falling market unpleasant, so it makes sense to hold a level of risk the investor can genuinely sit through. A strategy that relies on them staying calm won't help much if they can't.
Consistency
The habits that support good outcomes are ordinary ones: investing regularly, staying diversified, rebalancing when the mix drifts and keeping an eye on costs. None of them depends on knowing what happens next, so being wrong about the future doesn't undo them.
Rebalancing is a good example. It means trimming what has done well and topping up what hasn't, which feels wrong while a market is running, and that's a large part of why it helps to have it as a routine and not a judgement call. It can bring dealing costs and, depending on how the investments are held, a tax charge, so the routine needs to allow for that and not rebalance for the sake of it. If it's been agreed in advance how a portfolio is structured and when it'll be reviewed, a bad week in the headlines gives the investor less to react to.
Staying invested over time
Returns compound, and compounding works best when it's left alone. Interruptions can cost more than they seem to at the time, though that's usually clearer in hindsight. There will be poor years and some uncomfortable ones, and a portfolio built around the investor's own goals has a better chance of being on course at the end of them.
For internationally mobile investors, circumstances change more often. A move abroad, a new tax residency or a different source of income can all justify a rethink, and it helps to be clear whether a change is being driven by something in the investor's life or by the news. Only the first is a reason to act, and the second is usually nerves looking for something to do.
Views on markets are fine to hold, and a portfolio should change when the investor's situation changes. Most of the value, though, sits in the things within reach: how much risk is being taken, how well spread the investments are, what they cost and whether the investor leaves them alone when it's tempting not to.