Action on mouse button up

My script is supposed to deactivate a variable every time the left mouse button goes up. For some reason, my script sometimes 'misses' running that part of the script when i let go of the left mouse button, and some times it works. I had it print a counter every time it ran that part of the script to be certain.

I have the script in the Update() function and have even tried the FixedUpdate().

In my game it is integral that the player have full control of the scene by holding down and letting go the left mouse button.

How can I write the script well enough to be certain that every time the left mouse button is held down and at a decided time let go that unity will not miss an event?

Thanks a Ton!

Definitely don’t use FixedUpdate, because it doesn’t necessarily run every frame, and can miss events if they happen during a frame when FixedUpdate is not running. I’ve never seen an event missed if it’s checked in Update.