I can do all things through him who strengthens me. (ESV)
This verse is probably one of the most quoted Scripture verses in the entire Bible. Very likely you have even memorized this verse as a child. Like all verses in Scripture we need to be very careful to interpret it properly and in context with the verses around it. The best thing to do when reading a verse is to read the verse before it. That will give you insight as to what the current verse is saying.
Let's talk for a moment about what this verse is not saying. This verse is not saying that things that are impossible now become possible because God gives you strength. If it is God's will that you should have a fatal disease, repeating this verse as many times as you want will not make the disease go away. You also cannot gain special physics-defying powers just because this verse says, "I can do all things."
The context of this verse comes from the prior verses which describe Paul's circumstances. He has lived through times of abundance and times of need. He has been hungry and he has been well fed. He has had all kinds of circumstances. This verse is about enduring all things through the power that Christ provides.
We need to be careful that we do not use Scripture verses as magic tokens that we cash in to get what we want. This verse is about endurance in our walk with Christ, not a promise for us to have things that are outside of the perfect, sovereign will of God. We can, however, be very thankful that we do not ever have to go through things without God's powerful presence.
What are some circumstances that seem unbearable to you? Financial worries? Sickness? An over-bearing mother-in-law? You can endure because you can do all things through Christ who strengthens you.