Christians can go for a long time without having any evidence that what they do achieves anything. I’m currently using a prescription drug that has a 70% efficacy rate. That doesn’t sound too bad — unless you’re in the 30%. A lot of people you attempt to influence will be in the 30%, and it’ll be no fault of your own.
Furthermore, the visible 30% that you fail with will stick in your mind much more than the 70% you inspired to be a little better — but will never know it. I suppose that’s just the way life is, so try not to trouble yourself over the 30% (or whatever your “rate” is). Be assured that there’s a 70% out there made better by your devotion and holiness. Give God His due, and keep glorifying Him every day. People will be influenced and affected by it.