Draw out concerns earlier with a WideChart
When you create a WideChart, you're setting out a vision for the future. You're saying "I think I can see the future and this is what it looks like".
Creating a WideChart sets out your expectations and when you present these to other people, their first reaction will be to evaluate the timings and see if they feel realistic to them. Will you get people questioning your end dates? Will some people gawp at the timings you've set out? Perhaps, yes. And you shouldn't be afraid of this.
If there's a time to draw out concerns, it's at the start. In a customer-facing environment, getting someone to vocalise their concerns early on can be a tremendous help in closing a deal. In a vision setting environment (such as a leader laying out a strategic vision) getting staff to air their concerns at the start can help to clear the air, and also give you something to lean on throughout the project.
A WideChart is, by definition, a high-level, and therefore fairly a rough timeline and typically they only have 1 or 2 key dates. In pre-execution phase of a project, this kind of timeline is often the most realistic you can expect, but that's not the same as saying it will become reality. This is an exercise is visualising the future and aiming at a goal.
So don't be put off by people questioning your WideChart - this is part of what it's for!