Great responses thus far to what actually at first believed was 1st world, 3rd world problems easy answer. That is of course to say first be grateful life is so good your only stresses are "which knife to choose in the morning". Being the majority of the world population is at poverty level and they are stressing "will I get 3 meals today?" and "will there be enough water" or "will some disease take me out like it did a few of my neighbors?".
However, after pondering this further, I do realize it is an issue we are blessed with once we have acquired a good amount of knives we actually love. I don't suffer from this issue much anymore but did at some point. Having around 14 prized folders at the time I'd take a knife for say, an outing on the lake, that was very capable and yet at times thought about all the good ones I left behind. Very crazy and actually was so much of an issue that decided to trim the collection to only about 7-8. Sold that knife off even though still love it and would buy again if the opportunity arose (now discontinued) however had to make the tough decisions and comparing which knives I liked more or would use more. Usage and also rarity took preference. Now most all my knives are either limited editions, hard-to-come-bys (rare pieces) or ones I know I have or will use.
Anyone who wants to thin the herd so to speak can do a few simple tricks. One is to put away those knives in a drawer or somewhere out of sight for a minimum of a month with longer duration even better, say 3-5 months. Then when that time comes and you take the knife(s) out again, note 2 things. Note how much you missed the knife (how often did you think of it when you couldn't see, hold, or use it?) and how strong was your reaction when you finally unveiled it after the given time? Strangely, I've had reactions of "oh I'd never sell this knife". Then months to a year later, off it went as part of a future trimming session. Another trick you can use is the look-back-after-year trick. Use this reflection to take an honest look back over the year how much you used the knives and if this is important to you. For example I had one gorgeous, very rare early edition of Chris Reeve knife. I spent years hunting the knife down until finally got lucky. I swore I'd never part with it. Then a year or two later someone made me an offer on it couldn't refuse. Just months before though I examined this knife and found that as stunning as it was, as great and capable as it was, I only carried or used it a handful or 2 handfuls over the past year. I would almost always grab other similiar knives that were just as capable. Thus off it went.
If you are a pure collector and not a user, then good luck trimming the collection as have no advice there.

In the end be grateful if our only anxiety is over which knife (or car, or whatever) to choose for the day.
