Especially with foam tips, getting that perfect seal is an art and it takes time, only to be ruined by:
"Hey.....hey.... HEY!!...." with painful hesitancy, you pull out one side of your in-ear monitor, awaiting the important dialogue to follow.. "What was the name of that youtube video?"
Apparently someone at Shure was just as much annoyed as I am in such situations and have included a Push-To-Hear unit on their top of the line IEM's.