My first serious hillclimb, and a stupid error

When I decided I was going to ride this road, I looked at the Strava segments and selected what I thought was the bottom to top segment, which had a KOM time of ~19 mins.
I thought to myself “I’m nowhere near as fast as those people, but I should manage it in about 35-45 mins”
The segment I looked at was only for the steepest part of the climb, less than 1/4 of the total - and having planned for a 45min climb and quick descent, I hadn’t taken any food, gels etc and had only one water bottle.
It was a long and very hard climb, in 30*C temp, thankfully at the top was a lovely old couple who had driven by me on their way up who gave me a bottle of water when I asked if they knew of anywhere to fill my bottle.
Pretty dumb mistake, and a sign of my stubbornness to get to a point of realisation that I was wrong about this climb and say “too bad, you finish what you start. Rule 5 - HTFU”
Must say though, after it all I I was pleasantly surprised after the fact to see over 1000m of elevation gain

Damn, 2.3 straight hours of climbing at that temperature sounds like hell, although that descent must've been some sweet relief.

It's all undulating hills where I live, with the only large elevation change hills having stupidly steep descents which I can't enjoy, and short but painfully steep ascents :(.