There are many times in one's trading career where profits will be missed. That one big winner that got away will be an unavoidable part of your trading. Now, sometimes there is nothing you can do about it. It was a rare move that just doesn't happen that much. Other times it may be that your emotions got the best of you and you closed out a winning position too early.
Prior to even getting in a trade, how can we tell if we should be expecting a large profit or a smaller, faster profit? Truth be told, there are really great times to take a lot of smaller, winning trades, and then there are very good times to sit back and just let the market do the work for you while you wait for the bigger score.
One thing you can look at is the overall volatility of the markets. If you are a day trader then I could imagine you have a few quotes, or charts on your screen and just by looking at the movement for a seconds you can see if things are moving slowly or if there is some kind of activity. As of this writing, day traders have seen very slow moving days and are forced to take the quick, smaller target.
Another thing you can do is look at the index that you follow and see if it is at a potential turning point, or close to breaking an area that technical traders use. If the index has pulled back for many day's and now is at a known support area, you might enter trades with the idea that it could be a reversal day. In this case you would hold for the bigger move.
This is a very important art to learn if you are a short term trader. Knowing when to ride a trend or exit quickly is a skill that you learn over time. Done properly, it could mean a much better, and lower stress career.