Finishing a task without making any excuses. Just do it!
It's common for people to make excuses for themselves, especially when trying to wiggle their way out of the certain responsibilities. These excuses will oftentimes involve the conjunctions if, and, or but. For example, a parent might order their child to find a job, but the child creates an excuse and says: "I want to, but it's just too hard!" Or perhaps a kid is asked to take out the trash, yet instead of doing so the kid responds: "It's dark outside and I'm tired, so I'll do it tomorrow." See what I mean?
Thus, since these three conjunctions are often associated with excuse-making, I think this phrase eventually pieced itself together, deriving in some capacity from people who grew tired of hearing excuses being made so frequently by others. They didn't want to hear any ifs, or ands, or buts; they just wanted things to get done!
The phrase is at least over 150 years old, as it has been used in various works during the 1800s. For instance, the expression was written in the New York Daily Times newspaper from the year 1854:
"No ifs or ands or buts about it."
* Our entire family will be visiting an expensive restaurant tomorrow for dinner, so you better be there Gilbert, no ifs ands or any buts about it, and I mean it!
Note: The origins for most common idioms cannot be said with a certainty. What's provided are theories that may be plausible to how a phrase originated, but not necessarily so.
In addition, quotes that contain a phrase may be taken from old newspapers, poems, or books that were written centuries ago, but this by no means shows they originated from these. In all likelihood, if an expression is being used in a newspaper, it's probably already well known, and thus, from an older period of time.
Phrases and Idioms
knowyourphrase.com - The Meanings and History For Popular Idioms and Phrases | Use this handy list of phrases to search for more!