The shampoo effect is an interesting phenomenon wherein you maintain being drunk or high or whatever with minimum effort if you keep constantly drinking or dosing, even in normally small and ineffective doses. As per Urban Dictionary's Definition;
A residual drug or alcohol phenomonon in which, during a period after a heavy binge, only a small amount of the recently-abused substance is needed to re-activate your buzz. So named after what happens in the shower when you "rinse and repeat": only a tiny bit of shampoo is needed the second time around to achieve a full sudsy lather.
And an example:
"Man, I've only had one bloody mary and I feel buzzed!"
"Shampoo effect, dude. You were blasted last night."
So where does this leave us on the personal gain front? Well, the same effect can be observed doing anything that takes any amount of effort repeatedly. Most of us have something they want to achieve outside of their daily work commitments. I know I do. In fact, I used to be plagued with self-doubt, and what a friend and former colleague used to call Ship-o-phobia (Urban Dictionary definition pending), not to be confused with Ship Phobia.
So, firstly, what's the solution to that paralysis? It was simple enough for me: Just start.
OK, sure... but what then? The Shampoo Effect of course! A little bit more effort yields a multiple of that effort's output back. For me, that meant that even putting in only 30 minutes a day on my side project resulted in significantly bigger gains than attempting to work through the night from a cold start. A nice side effect of this is that it has become easier to continue working on my side project than to stop.
I've seen this phenomenon in different guises before, the first and most obvious will probably be Jerry Seinfeld's chain philosophy. Another take on this focusses on habit-theory and how something like the shampoo effect actually has a reduction on cognitive load over time, thereby making it easier to maintain your productivity-lather. SeriousPony has a great take on this, and the amazing people at wellness startup Lift drop some serious science. Both worthwhile reads in understanding why we work the way we do, and how to do it better, easier and for longer stretches.