This story has been told to me in a couple of different ways the first time was in a book where the monks were Desert Fathers of Early Christianity, and the second time they were Japanese Zen Monks! but that has been the only difference in the two renditions I noticed!
3 monks who were close friends were sent out into the world too live with the Laity.
As they were walking on the path away from the Monastery they came to the top of a hill where they could see the town and surrounding lands including a Forest!
They decided to rest for a while and got chatting about what they were going to do next!
One decided to go to the town and help the sick in the hospital, the second decided to go to the town and help the homeless, and outcasts, the third decided to live in the forest!
The first two were shocked at this thinking to themselves how selfish the third monk was, and they all went their separate ways, after agreeing to meet up in one year!
After the year had past, the monks met!
The first monk complained about being tired, his feet hurting from standing all day every day, and feeling depressed hearing how much pain the patients are in every day!
The second monk complained about being depressed due to hearing all the terrible life stories of the homeless folk, and is in pain due to contracting a nasty disease from working in the Slums of the town!
The Third monk smiled and said he has has a great time, very peaceful, helping the occasional weary traveller, and hurt animal, or those who sought him out for help! has many friends whom has helped him with shelter, and food, and he helps when they need him! his life was perfect!
the other two monks realised that they took on too much and lost sight of what life was about! not going to solve the worlds problems, but to be ready to help people when they need it
This is from memory so a bit shorter or longer than the original?