The campaign goal isn't set by picking a number and hoping donors meet it, it's confirmed through the feasibility study by testing real prospect capacity and interest before the goal is ever announced publicly.
In practice, that means building a gift table (or gift chart) that maps how many gifts at each level are needed to reach the goal, typically led by a small number of large leadership gifts at the top rather than a large number of small ones. A widely used rule of thumb is that roughly 80-90% of a campaign's dollars come from the top 10-20% of donors.
Catapult confirms that structure during Campaign Planning, prioritizing prospect data and building the detailed gift table and timeline the Quiet Phase will run on, so the number isn't aspirational, it's tested.