McMillan wants to lift the club out of the inconsistency that has marked their play in recent seasons.
He told The42.ie that while Munster has achieved some memorable highs, it is their low points that are the issue.
"It almost seems to be ingrained in the Munster psyche that when our backs are against the wall, or when we get into really big games that matter, we have the ability to go to another level.
"That's admirable, but we can't have those days, and then the next week turn up and lose to the team that, for all intents and purposes, we should beat.
"It's about not necessarily judging ourselves on the days when we're at our best. It's about judting ourselves when we're at our worst."
McMillan illustrated his point by using the example of international Tadhg Beirne.
Beirne at his best played at a 9.5 out of 10, but even on an off day, he was capable of a 7.5 effort.
"It's trying to achieve that with a good rugby team, where your best day at the office is a 9.5, and a poor one is a 7, not a four or a five.
"If you're at 7, you still give yourself a good chance of winning that game. It's about getting everybody's level a little bit higher. Raising the floor instead of raising the bar."
One area he is keen to address is the Irish tendency to focus on negative outcomes and overlook the positive ones that also occur.
Many of the regular Munster coaching staff have been retained, although McMillan has former Chiefs manager Martyn Vercoe and their head of athletic performance, Brad Mayo, alongside him in Ireland.
"Everything that we are doing good, I don't find any reason to disrupt that, but it's also my job, and one of the reasons why people brought me in, is to be a little big of that disruptor – to bring a different set of eyes and look at things a little bit differently and to challenge the way things are being done.
"That doesn't mean that we have to change. It just means that we may have to think about the opportunities we may be missing."
McMillan said the Munster management is a highly functioning coaching group. He doesn't want them to agree with everything he says.
"I want to be challenged. The other assistants need to be challenged. Out of that, we will look at the game a little deeper and want we need to be successful."
McMillan is also continuing his Chiefs practice of working closer with the side's supporters and has been visiting different areas of the region for training sessions.
He also wants to see Munster players promoted to playing for Ireland.
"Having robust pathways, talent ID, pathway systems, and growing your game from the bottom up is important. That's my basic philosophy around rugby, how to get people to the next level.
"Leaders create culture. Culture is driven by behaviours, and behaviours determine outcomes.
"We're driving hard standards and behaviours that will keep us in good stead when we're under the blowtorch on game day. That has to be driven by myself."