It is a sad thing to meet pilgrims on the Camino whose topic of conversation is based on fear. Fear of being late, of missing the flight, of getting injured and having to hobble in pain rather than rest and recuperate.
The thing is - you cannot predict it. It may rain and be ridiculously cold up in one of the three mountain ranges (Spain is the most mountainous country in the whole of Europe after Switzerland!) and this can slow you down. Also, things happen along the way. You may visit a church and become entranced and want - need - to go to the morning service. You may meet someone in distress and need - want - to slow down and help them. You may find a stream at the bottom of a small valley with bars of sunshine cutting through the trees, a tiny wooden bridge, bright blue butterflies dancing around your ankles, the clear sound of an almost eternal stream and a soft grass bank, where you can stop and soak your feet and just - BE - and then fall asleep, to wake so much later than 'your plan' with its flight at the end allowed. The pilgrimage can be a glorious thing - it is, but this includes the pain and if you get a shin-splint this will really stop you walking for a day or so. If you have to arrange a flight home then arrange one that leaves days to spare (you can always bring it forward). Then in Santiago, once the grime is off, you can sit and watch other pilgrims coming in and reflect, deeply, upon what you have just done, of all the billions of people on this blue pearl we live on, just a few, a very few, get to do this. If you are planning to go, for whatever reason you think you are doing it - God has called. Go. Return home when you can. And don't be afraid, the medieavals had to walk back as well!