There's a reason the first draft is called the "first draft." After marinading in a drawer for X number of days/weeks/months/years, returning to the text with fresh eyes lets you see the mistakes, the repetition, the missing dialogue, the dangling threads--all of which must be tweaked, pruned, buoyed, buffered, hacked, slashed or murdered, whether darling or merely an innocent bystanding thought. Some of this is obvious, glaring off the page as if written in scarlet ink, and other hidden ninja stealth goofs need a bit of time to weed through. Hence, the tangled analogy.
Any parent knows that when it comes time to comb a kid's hair, the beginning stroke is usually okay; starting at the scalp, the comb pulls gently through--no tangles or tears yet--and it's only when we hit the first snag that it becomes painful, the loose ends are wrapped around other threads, become knotted, hard to follow, and resist all attempts to pull free despite the sweating and swearing and tread perilously close to wanting to cut the whole thing out altogether, and sometimes this happens. (To the manuscript, not the kid's hair. Be real. Unless gum is involved because then all bets are off.)
Back to the analogy: the first edits come easy, but as soon as you begin reworking something that clearly needs to go, you realize that all that interconnectivity you praised yourself for all those days/weeks/months/years ago now comes back to haunt you because now it *all* has to go, or be rewritten or reimagined and even though this is a dark, dark time and the scissors beckons from the drawer, listen to yourself, be patient, be kind but thorough, and know that in the end, this will all work out for the best and it will be even better than it was before.
Just like a new haircut. Trust me--it looks good on you!