1 Thes. 2:1-2 (ESV)
For you yourselves know, brothers, that our coming to you was not in vain.  But though we had already suffered and been shamefully treated at Philippi, as you know, we had boldness in our God to declare to you the gospel of God in the midst of much conflict.
You never know. You never know what the result will be when you speak the Gospel, when you declare the Gospel. At Philippi Paul and his cohorts were ridiculed and persecuted for it. In Thessalonica they were received with joy, yet in the midst of much conflict.
Sometimes you play it over in your head. That time you shared the gospel and were rejected. You wonder what you did wrong. Maybe nothing. Seriously. The Gospel is the gospel and not all who hear it will believe. Sometimes I am dumbfounded. Someone I shared the gospel with two years prior shows up at church, or calls me out of the blue. Sometimes I say something so simple and I think this person isn’t going to buy this, he is too hardened for that. Yet they do. Shows you what I know. I am not good at discerning hearts. Not for me to do. Declaring the gospel that is what God has given me to do.