I've seen a lot of 100-day plans. And the thing they almost all have in common is that they were built by people who won't be around when it gets hard.
Not laziness. Not bad faith. The advisors who build them are typically smart, well-intentioned, and trying to help. The problem is structural: the plan is created during the deal process, when the pressure is to demonstrate rigour and show the investment committee that there's a credible operational thesis. Then the deal closes, the advisors move on to the next one, and the management team is left holding a beautifully formatted document that was built around a version of their business that no longer quite exists.
What goes wrong
The most common failure mode isn't bad ideas. It's volume. I've seen 100-day plans with 40 or more initiatives, all competing for the attention of the same small leadership team, all marked as priorities, none of them properly resourced.
The result is predictable. Nothing gets done well. The team spends the first quarter in planning meetings about the plan rather than executing it. Momentum, which is the thing you most need in the first 100 days, never builds.
The best plans I've been involved in focus on three to five initiatives. Enough to show ambition and build credibility with the new investor. Not so many that the organisation can't absorb them while keeping the existing business running. The test I use: if you had to cancel everything except three things, what would you keep? Start there. Everything else can wait.
The second failure mode is underestimating disruption. A change of ownership is unsettling, even when it's broadly positive. Senior people spend the first weeks watching rather than executing. Middle management goes quiet. The management team that looked confident and aligned in the data room is now managing their own anxiety about what changes, while simultaneously being asked to deliver transformation. That tension is real, and the 100-day plans that don't acknowledge it tend to stall in month two.
Quick wins matter. But they need to be valuable, not just visible. Renegotiating a vendor contract that saves £200k annually is a meaningful quick win: it compounds, it signals commercial judgement, and it gives the management team a win to talk about internally. Rebranding the company intranet is not. It might feel like progress. It isn't.
The thing that makes a difference
The most effective 100-day plans I've seen were built with the existing management team, not handed down to them. That distinction sounds obvious but it plays out very differently in practice.
It means spending the first two weeks almost entirely listening. Not presenting. Not assessing. Listening. Understanding the real dynamics of the business, not the data room version. Because the data room shows you what the business looks like when someone has curated it carefully for an audience. The first unguarded conversations with the people running things tell you what it's like to work there, where the real friction is, and which of the stated priorities are shared versus politely accepted.
Get that right and everything else gets easier. Get it wrong and you spend the next six months wondering why a perfectly good plan isn't working.