More generally speaking TCOI means to get things done or to accomplish something. Also, to get "get the ball moving" or to work at a goal without hesitation. Results are more important than method and desired results are a must.
When it's most important to TCOI or may take even more effort than normal to accomplish a TCOI mission someone might suggest you "Attack!" a TCOI which later evolved into ATACOI. This usage is only recommended for long term TCOI users.
It may also be used alone in acronym form.
The opposite of TCOI is fail.