Small hits or losses are alright, so long as they aren't persistent or don't last forever. That said, we cannot take 10% or even 5%, losses ongoing and forever. Even if we under-perform the markets by a few percentage points, we can lose out on considerable gains once the power of compounding sets in.
Big losses are a different story. We can tolerate the 10% corrections and even ignore the 10% twitter, but if we are exposing ourselves to 50% losses on individual investments - or worse, on substantial portions of our portfolios - look out! It will take a lot to turn that ship around and get it back to where it went off course.
Fluctuations, minor corrections and bear market
There is a big difference between fluctuations, minor corrections (considered to be 10% pullbacks by most market professions), and an all-out bear market, usually considered a plunge of 20% or more. The prudent investor senses the difference between fluctuations, corrections and the more destructive bear markets.
The high cost of an untimely hit.
Volatility can be expensive, especially, if it goes beyond normal investment noise into creating a significant downturn, especially at the beginning of an investing period.
The principles and effects of compounding makes a difference not just how much we succeed but also WHEN we succeed in the markets.
The general principle is that the more we can earn SOONER - to unleash the power of compounding to a greater degree over a longer time - the better off we are.
Conversely, if our investment capital takes a hit in the early going, it takes a lot just to get back to even, let along to get ahead.