You are definitely not alone in this. The old adage "Buy low and Sell high" is much easier said than done. First of all timing the market is impossible and secondly, like you described it's hard to take the emotions out of it. There's been several times I've missed out by selling too early - afraid it would drop and I'd lose money and buying too late - seeing an asset climb and not wanting to miss out, as well as holding too long - thinking there's now way it could lose more than this.

I try to let go of what could have been (though sometimes I still daydream about it) and move on to what I can control and try not to let my emotions get the best of me.