Lent is a quarter gone. As usual this year, I gave up chocolate.

Unusually, I am still succeeding at this stage in this fast.

The reason for breaking the fast in past years is simple.

I like chocolate.

So every Ash Wednesday for the past 10 or 20 years, I've made a desultory attempt to give up chocolate. I've felt good and Christian about it. Maybe even written a column about it. Then after day two or three – sometimes after even less than a day – gone out and bought one of those golden bunnies. Or a box of Belgian seashells. One year, I just simply forgot and it was Lent and ate the bunny before remembering.

But this year, something has changed.

A quote from the model Kate Moss once made a big impression on me. 'Nothing tastes as good as thin,' she said. For people like me, that has simply never been the case, but I got what she was saying. And now, the equation has turned around in my head.

I'm simply fed up with failure.

In the modern age, and the feel good society, we don't hear much about God's anger. Certainly I don't like to think about it too much. But when I'm angry with myself, that's when I allow myself to go down the awful road of imagining the wrath of God. Of course he isn't sitting up there on a cloud threatening to send lightning bolts down upon me if I stray down that tempting seventh aisle in Sainsbury's. But if I can't even succeed at something as simple as forsaking chocolate for 40 days, what about the big things? All our actions contribute to the common good in our local communities and beyond. If I lose discipline over things such as a Lenten fast, what knock-on effects might that have on acts of service for others? And how might that feed into overall neighbourliness?

I'm certain God does get seriously angry about the big things that mankind gets wrong.

And then there is the small question of 'sin'. Again, not a fashionable concept in the modern era.

As friends of mine say, it's not the mountains that trip us up, it's the matchsticks. Doing something small for Lent, daily acts of self-discipline, creates the good habits that helps us when it comes to the bigger tests. And, countering that, small acts of sin might not seem such a big deal. But we all know they add up.

And keeping it in the day really helps. The late, beloved Billy Graham got this right, as so much else: 'Take one day at a time. Today, after all, is the tomorrow you worried about yesterday.'

So although giving up chocolate feels small, and is small, such small things add up to make big things – terrifyingly big things. Paul wrote to Timothy: 'For the spirit God gave us does not make us timid, but gives us power, love and self-discipline.'

This Lent, I pray, I will not fail.

But then what? Failures of self-discipline do have their rewards. If it is not the taste of chocolate, one reward of failure that I am horribly familiar with is the escape from the responsibility of success.

So how to deal with success? That, perhaps, is the most terrifying thing of all – and what I will try to address next week.

Ruth Gledhill is multi-media editor of The Tablet and an editorial adviser to Christian Today. Find her on Twitter @ruthiegledhill