Tl:dr; someone close to me did something ambitious and made mistakes. The feedback they got was significantly to harsh: not because it is false, but because it discourages trying again.
This summer I had one of my most disheartening experiences with the EA community and I think this is really important criticism. So, if you are a grant-maker or know someone who is, please let them know: how you react after a high-risk, high-reward project panned out not to work, will determine how likely it is the people involved will try again. Fact is, we are lacking ambitious entrepreneurs who can start large projects. Any action that could lead to less of those should be handled with care and the feedback from funders after a project is one of them.
I won't give more details and the person in question has really good support, so I think this specific instance is fine. But if the pattern of response remains the same, I can imagine many highly promising people being burned or becoming disillusioned. Be empathetic, try to model how it must feel to try something big for the first time - especially if the grant recipients are young - and then react accordingly. Criticism is important, but the wording is too. And if something really was harmful, then at least have the courtesy to wait a while till emotions have calmed down and the people involved had time to process what they did on their own.