Not all pastors stay the course. It's a fact of Christian life. I have a photograph of the students at Bristol Baptist College, where I trained a good number of years ago. We all expected to spend our working lives in pastoral ministry; very few of us have. We've gone into chaplaincy, denominational or academic appointments, and in my case religious journalism. Some of us remain Christians but not pastors; others lost their faith entirely. There were some moral failures.

Not all of this is a bad thing, though some of it is; God moves us on along unexpected paths. But what's really sad is when people feel they can't cope with the demands of the role. They try, increasingly desperately, but the mismatch between what they can give and what they feel they ought to be able to give becomes too much. That's when the expression "burnout" comes to be used.

And it does happen. US megachurch pastor Pete Wilson, formerly of Nashville's Cross Point Church, announced his resignation on September 11, saying he had been "leading on empty". "I'm not okay. I'm tired. I'm broken, and I just need some rest," he said. More than that we don't know. Wilson's announcement made headlines because he's quite a prominent pastor, but most burnt out cases don't. They get out if they can, or they drift along, sad and disappointed, no good to their congregation or themselves.

There are some circumstances where pastors face hard times and it's because of problems that have nothing to do with them. If there are damaging congregational battles, or the building's falling down, or money's too tight, that's a different story. But sometimes everything seems fine on the surface – and it's not.

So why do pastors burn out, and what can be done about it?

1. They can ask too much of their congregations

Some pastors are unhealthily focused on creating a certain kind of church, based on what they think a congregation ought to look like. Every minister has a responsibility to lead his or her flock in growing into Christlikeness, but that doesn't mean everyone in the church is going to look the same. Sheep look pretty similar to non-shepherds, but the shepherd can tell each one of them apart. People are individuals, and they're resistant to being told what to do or how to think. Try to create a church in your own image and it will probably defeat you.

2. They can forget about Jesus

Ministry is hard. The Bible is a difficult book. People are difficult too (see above). The emotional demands of caring for people when they're in desperate need, as sometimes they are, can be exhausting. It can seem like a treadmill, on which you labour unceasingly without getting anywhere. Church members disappoint us. The pastor wonders whether it's worth it.

You can't avoid times like that. But Matthew Arnold's poem 'East London' reminds us where to look for refreshment. The poet describes a walk through the "squalid streets of Bethnal Green", continuing:

I met a preacher there I knew, and said:
"Ill and o'erworked, how fare you in this scene?" -
"Bravely!" said he; "for I of late have been
Much cheered with thoughts of Christ, the living bread."

Pastors don't minister to achieve a particular end, but to serve a particular person. Without a personal commitment to him, they'll inevitably fail.

3. They can stop taking care of themselves

The idea that every moment of the pastor's time has to be devoted to the church is a form of pride. It's a way of saying they think they're indispensable. Martyrdom – sacrificing everything to a congregation – can be a very specialised form of boasting.

It can also lead to burnout, because no congregation will ever quite be able to match up to the standards of a really expert martyr. The chances are they will become tired, then resentful, then bitter. They can avoid this by taking care of themselves. TIme out is essential. So is decent food and exercise. A walk in the country or an unscheduled afternoon off is OK. So is reading a book that has nothing to do with theology. These things are good for you, and good for the congregation. They make you a more interesting person.

4. They can get in the wrong race

Wise pastors know they aren't in a sprint, but a marathon. If one sermon bombs, it's OK – there'll be another chance next week. It's not up to you to fix the church, it's up to God. Bad behaviour in your congregation is no reflection on you. Mourn for it, but don't obsess over it.

Good pastors care deeply and are hurt when things don't go right. But faithful pastors learn to hand the responsibility over to God, and keep on keeping on.

Follow Mark Woods on Twitter: @RevMarkWoods