Paul had the confidence that as God had been with him in the past, He would be with him in the future. Therefore, he wasn't paralyzed by fear from transient problems or temporary setbacks.
For example, I have much invested in my family. There has been the years of working with Aaron when he wanted to quit judo, drop out of baseball, the times when the police called about some junior high hoodlums skateboarding on the Hilo College campus illegally, and the late nights at the Emergency Room waiting for the doctors to patch him up from rollerblading or surfing accidents. Now, he might have a broad assurance that I'll not abandon him. I have too much invested!
In a far, far greater way, God has done the same with me. He has invested years of mercy, years of grace, and years of His patient discipleship in me. God has had to protect me several times on the road and in the ocean ... and I am sure He had reassure discouraged angels wanting to abandon their assignment God gave them to keep watch over me. I can walk with constant gratefulness and with much confidence that what He has begun, He will perfect!