Worst decision was not trading for a good QB late in the season with a lot of depth at both RB and WR. Not fully planning out matchups for the Super Bowl week in advance of week 14 and losing because of it. (Typing this to try to reinforce it for the rest of my fantasy life...)
Specifically... deciding to pick up and then go with Tannehill even with the arguable weather. Not that I had any other good options at QB (see above).
Sticking with Andre Johnson at WR in hopes "the stud" would pan out one more time, despite common sense, instead of giving Alshon Jeffery a chance.
Not having the courage to plug in Alfred Morris in a game that made sense he would have a lot of opportunities, and sticking with Moreno, in the hopes he would get a big score and not sit for a lot of the game. Not much of a difference in the end... but you asked...
In short - it NEVER is time to rest on your laurels and avoid getting better through planning and preparation. And... sometimes the other team just has a better week.
Sorry for the rambling response. Just a disappointing week, as many will have. If I could do it again - would probably do it the same, except for the laziness earlier in the year.