You are either a pioneer or a follower; you can't be both. And if you are a pioneer, you know all about worry.

If something has been done before, you know it's possible. If you don't know something is possible, you worry about it.

I'm about to embark on a swim with significant risks and consequences - financial, reputational and environmental. So there hasn't been a night in the last month that I haven't woken up.

A few nights ago I was using the worry hours to plan, and remembered something Mike Tyson once said: "Everyone's got a plan until they get punched in the mouth."

I have a plan to try and swim 10km per day. But when I swim into my first bloom of jellyfish, that plan will become flexible.

I know that I'm going to get sunburnt. I'm going to be frozen, I'm going to be stung, and I'm going to become mentally and physically exhausted. Have I done too much preparation, or not enough?

What if we get the tides wrong, get caught in a counter eddy and find ourselves going backwards? This is a notoriously dangerous coastline, with the shipwrecks to prove it.

Did I mention that half my expedition team is new, and half has no sailing experience?

In those waking worry hours I also remembered the Stockdale paradox.

Admiral Stockdale was an American pilot who was shot down in Vietnam and spent eight years in a POW camp. He said that the people who survived had two important qualities.

First, they always believed they would be freed. Second - and this is the paradox - they had no optimism. Because the people who did have optimism - the people who hoped they would be free by Easter, then by Thanksgiving, then by Christmas, and had those hopes dashed over and over again - those people didn't survive. The people who survived were the ones who confronted the brutal reality of their situation.

I have to face some brutal facts when I look at the chart of our 560km swim route. This is the longest swim anyone has ever done, adhering to Channel Rules in water this low temperature. I honestly don't know how I'm going to do this. But I do believe I'll see the white cliffs of Dover. So that's the paradox that's going through my mind.

The swimming is only part of the challenge. We've also had to co-ordinate with sponsors, raise funds for the expedition, recruit the right people for the team, and deal with the media... all the while juggling private lives with unexpected domestic crises.

As if all that wasn't enough, after six months of campaign planning and preparation, we learned that Donald Trump is coming to London on the day I start swimming. We certainly hadn't planned on such a big media story distracting from our message.

Because the message is the reason I am doing this swim. The truth is we are failing our oceans. And it's only through bold and courageous action that we're going to be able to protect them properly. "Piecemeal" protection is not going to safeguard our seas. We need an enormous shift in business and government and the public to be able to do this.

There are challenges ahead. But as English Channel crossing pioneer Captain Webb said, nothing great is ever easy.