I learned in my first adventure that what I've prepared to happen might just be stupid and unrealistic, so I'm never too attached to it. If the dice say it doesn't happen, they know better than me, so I just toss it. If I lie about the dice to make it happen anyway, I'm making a worse experience for everyone.

If a failure means a path is unavailable, see if you can open up a different path. If there are no other paths, just let them have this one for free.