The title of this post is the famous quote from 'Old Partridge' in Reminiscences of a Stock Operator, the fictional biography of Jesse Livermore.
The charts I've posted of various indices below clearly show that, even with one or two speed bumps along the way, the trend has been up for several months now, and that trying to initiate trades going in the opposite direction (i.e. trying to pick a top of this move) would have resulted in consistent losses.
Even if you do not apply a trend following strategy, simply observing charts such as these, and using them as a basis for determining your directional bias towards your own positions and methodology will ensure that you are trading along 'the line of least resistance'.
If you ARE following a trend following strategy, then all you need do is hold your positions when trends such as these become apparent, and resist the temptation to take your profits on the basis that "the markets have gone up too far" or "the markets are overbought". How would you feel if you did that, and the Dow went up another 1,000 points, for example? Simply observe price and see where it takes you.
One thing I have found with less experienced traders trying to utilise such a strategy is that, while they can easily grasp the principles of entering a position, the exit presents a bigger problem, especially when a pronounced trend forms. For the overall expectancy in a trend following system to be achieved, you HAVE to let these big trends take their course and exhaust themselves - these cover all the small losses you incur and have profits left over, generating the overall positive return.