, lensman wrote

The use of !timer1.Enabled relies upon a quirk of the compiler.  It is not guaranteed to work 100% of the time on all systems.  Yes, it does today, but tomorrow may be another question.  I have been coding since the late 70's and have worked on systems where that statement would fail.

In C# it is not a quirk of the compiler. It is a guarranteed tenet of the language.

!true == false

!false == true

Always, on all systems, for now and forever.