The below paragraph is what I'm talking about. Context = The character is simply reflecting and extrapolating the meaning of some clues. "He zeroed in hard on these facts. They were a mess, for sure, and like a complicated puzzle even the pieces that seemed to fit belonged on different sides of the cardboard. Yet from the chaos, the basic shape of the truth was starting to emerge."
How about, He zeroed in on the mess of facts - a complicated puzzle like a double-sided jigsaw. Yet from the chaos... Leave out the idiomatic for sure, and cardboard just doesn't work for me. And check your tenses - started instead of was starting (to match zeroed.) Even that short paragraph can be tightened up. See if there's anything there that may help.
I don't see any problem with for sure if your writing style regularly uses idiomatic words or phrases. A funny (to me) aside: I asked my wife the same question about a paragraph of mine and she said "That's like me asking you if these jeans make my ass look fat.".
