There was a group of teenage boys around our age racing up to the top and jumping off. I fidgeted awkwardly, staring at them and at the cliff, wishing Millie didn’t have a broken arm so she could go first and tell me if it was fun.

Reading my mind, Millie nudged me with her elbow. ‘Go try it,’ she said, shrugging her shoulders, ‘it looks like fun.’

The spotlight was so rarely on me in our family that I balked. ‘But you can’t go,’ I pointed out, ‘I would have to go alone.’

‘So?’ Millie said.

‘All those boys are up there.’

‘So?’

‘Boys think you’re cool, but they’ll make fun of me.’

‘What makes you think that?’

I shrugged my shoulders.

‘Andi,’ Millie said to me sternly, at age fourteen already able to sound exactly like our mother, ‘if you think it would be fun, do it. You don’t need me to babysit you, and you definitely don’t need to care about them.’ She glanced at the boys with disdain, slightly sticking up her nose.

Something about the way she said it made me feel like she would think I was a loser if I didn’t go. I took a deep breath. I had never done anything without Millie before. She was always there, trying things first, making them look cool. I was comfortable following in her footsteps. But the jump looked so . . . fun. I kept staring.

Millie elbowed me again. ‘Just try it,’ she whispered. ‘You’ll love it, you’ll see. It’s OK that I won’t be up there with you. I’m right here. Show ’em how it’s done.’

I don’t know what came over me, determination or fear of disappointing Millie, or both, but before our parents could get back, I took a deep breath and charged up the stairs, launching myself straight over the cliff and cannonballing into the water below. When I got to the surface, Millie flashed me a huge thumbs-up from the side of the pool. I was thrilled.

For the first time in months, I felt like she wasn’t embarrassed about me. For the first time in months, I was proud of myself.

That trip was where our love of marine biology was born. Millie swam the whole time with her waterproof cast, awkwardly squeezing into life jackets and paddling with one arm, logging every fish she saw into a dive book.

That trip was where I realised I could do things on my own, without my sister. When I realised that when I did things that made Millie proud, usually I made myself proud too.