Jesus and the Apostle Paul both used the analogy of sowing and reaping. Jesus told a parable in Matthew 13 about a guy was scattering seeds.
I planted the seed, Apollos watered it, but God has been making it grow."
Putting those two passages together reminds us that we need to keep doing what we're supposed to be doing.... sowing seed. Or possibly watering it. But the results are up to God. It's only God that makes it grow.
So, if you are discouraged because someone is not responding the way you want them to when you continue to sow and sow and so, don't be.
God is not asking us to grow plants -- that's his job.
All he's asking us to do is to sow the seeds.
If you replace the word swimming with the words sowing, I hope this song gets stuck in your head not just today... but for the rest of your life.