There is no such thing as probability. All there is is possible and not possible.
I don't know how the point of the comment could be missed, but what I am saying is, it is a mistake, a rookie baby not-a-programmer not even any kind of engineer in any field, to even think in those sorts of terms at all. At least not in the platonic ideal worlds of math or code or protocol or systems design or legal documents, etc.
Physical events have probability that is unavoidable. How fast does the gas burn? "Probably this fast"
There is no excuse for any coder to even utter the word "likely".
The ONLY answers to "Is this operation atomic?" or "Is this function correct?" or "Does this cpu perform division correctly?" Is either yes or no. There is no freaking "Most of the time."
"Likely" only exists in the realm of user data and where it is explicitly created as part of an algorythm.
There are whole branches of computer science and IT dedicated to reducing the likelihood of unpleasant outcomes: cryptography, security, disaster recovery etc.
You cannot guarantee your public key algorithm is impossible to break, but you can use keys long enough that an attacker has an arbitrarily low chance of succes with the best known methods.
You cannot prove your program is bug free, outside of highly specialized fields like aircraft control, but you can build a multi-layered architecture that can reduce the likelihood of successful intrusion. You cannot prevent a EMP bomb from wiping all your hard-drives at once, but you will likely maintain integrity of your database for uncorrelated hardware errors.
"Likely" is a tool that works in the real world. If you will chase mathematic certainty, your competition will likely eat your lunch.
Where you might be correct is that "unlikely" is very close to "likely" in the particular topic of thread safety, you just need a sufficiently large userbase with workloads and environments sufficiently different from your test setup.
I have already eaten my competitions lunch through not being afraid of a little rigor, and not leaving a wake of shit that only works on good days behind me.
