You have ambitious goals but limited resources - that is the normal case, so to speak. You do your best and want to know if and how your best actually works and has an effect. In order to be able to do even better, if necessary. And to be able to show what you have achieved and its effects.
Resources for an evaluation are also (usually very) limited. With a mixture of standardised methodology, clear focus and individual design, we nevertheless produce robust results and without the evaluation becoming more expensive than the evaluated project or programme.