Sorry, I didn't make myself clear. Dealing with rejections takes time, you get distracted, you get sad, it kills time which can be put in much better use.
You can deal with rejections, but that doesn't mean you have to deal with rejections.
You can use the time to make your product better. Someone famously said "Be so good, they can't ignore you", being mediocre and spending time in those activities is not very fruitful.
Also, need to remember it adds up - YC, 500Startups, tech stars, etc. and then pondering about the results and then the sorrow phase after not being accepted.