The CrossFit mentality has developed itself into an "all out, all the time" mentality, and that isn't always the right approach.
Not every WOD should be a competition against the clock, yourself or others, although the environment is often created as such. Yes, it's good to challenge yourself, but there is a time and a place for it.
Let's highlight the 2 main differences.
These are the daily sessions, like met-cons, skills, drills and strength sessions. With these sessions you want to create the right stimulus, like getting stonger, more skilled, higher VO2 max, etc.
These sessions should make up the largest part of your schedule. An example.
Let's say the WOD is the following:
21 double unders
7 ring dips
7 toes 2 bar
There are 2 ways to approach this WOD:
1) You're not really good at double unders, but you want to have a fast time and opt for the single unders substitute.
2) Since it's "only" 21 DU's per round, you decide to train them and at least try to do as many as you can per round, or perhaps even all of them. Your time is not a priority.
This way at the end, you've trained 210 double unders with out even realizing it as much.
This is the time to test yourself after all your training sessions. Great testing opportunities are benchmark WODs , a 1RM attempt, etc.
Let's use the same example of the double unders.
Of course since you've been training your double unders recently under various circumstances, you've been able to string them together and can now aim for a nice fast time!
What it comes down to
Not every WOD should be approached as a "balls to the wall" session. This only results in frustation, burn-outs and half-assed reps at times, while it's more important and useful to utilize these WODs as a training tool.
Attack your weaknesses, create your own "Rx" within a WOD, so you can train and finish the WOD with a feeling of accomplishment.
Ask your coach for the possibilities, that's what they are there for!