I've found the problem isn't a player forgetting to use inspiration. It's a DM forgetting to, or being too distracted to give it out. The ONLY times (in recent memory) I can remember a player getting it (when I've also been a player) is when that player did something extraordinary or was spotlight hogging and REALLY got the DMs attention. That's my issue with it.
I liked the concept of inspiration when it first came out, but I find that I never use it even though I've tried a few variations. The reason to have inspiration seems to be to have a meta-game carrot in order to RP more. To encourage a person to play and act out their character. As the PHB states, it's used to "reward you for playing your character in a way that’s true to his or her personality traits, ideal, bond, and flaw".
But it's a metagame tool, which means that as we're playing as a DM I'm supposed to be constantly thinking of the metagame instead of just engaging with the players at the table. But it also means that I'm supposed to keep track of TIBF for all of my player's PCs. I can barely remember the PC's names half the time, how am I supposed to remember all of that? So not only can it be a bit immersion breaking for me, both as a player and DM, TIBF is often so vague that there's not much there. I mean, if my PC's ideal is "I work hard to be the best there is at my craft", what does the player or DM do with that?
Inspiration, along with TIBF are interesting concepts and I'm sure for some people they give the appropriate nudge or add to character concepts. I just find that they're always ignored.