I set the lawnmower on fire.

Well, not really me.  
And not actually on fire.
But that’s pretty much what happened.

Well, not really.  There’s more to it than just that, obviously.

This is what actually happened:
A fundamental design flaw conspired with a lackadaisical maintenance schedule to bring the machine to the smouldering edge of flame.

I guess that’s not really the whole story.  Either.  I mean, it’s rather lacking in details.  To put a fine point on it, there’s a lot more going in between those clauses than what the clauses alone imply.

Let’s start again.
The facts are these: the lawnmower is electric.  It has two counter-rotating blades; hence it has two electric motors – one for each rotor.  The electric motors are vented below the mower deck.  The mower has a “mulch” setting which chops the grass very fine and does not vent or throw the clippings beyond the mower deck.
Can you see what happened next?
Those fine clippings clogged the electric motor vents.
This has occurred for years without incidence.  And around once a year I pull out needle nose pliers and a screwdriver and clear those vent ports.
This year, I failed to perform this maintenance task before mowing for the first time.  Or indeed before the second time.  Or the third.

This was the situation as I began to mow last week, for the third time this year.  I was perhaps five minutes into the job when I began to smell a little smoke.
I thought, “Which of my neighbors is burning shit this time?”  Because all of my urban-hillbilly neighbors burn things which they shouldn’t be burning all the year ‘round.
The odor intensified, and I looked around again to see which one it was.  Nothing.  I shrugged and continued mowing.  About a minute later, smoke began to pour from beneath the mower deck.

After a half hour spent removing dried and smouldering grass clippings from one motor, and just dry clippings from the other, the apparatus had cooled enough for me to partially dismantle and diagnose.  Now, please recall from the previous sentence that I said one of the motors was clogged with dried and smouldering grass and one was clogged only with dried grass.  It turns out that the first motor was beginning to seize, overheating, and therefore setting alight – nearly – to the grass clippings accumulated in its vent ports.  Unlike its twin, which was as yet fully functional in spite of those same fine clippings.

Right from the start, right from my initial purchase of this lawnmower, I had looked at those electric motor vent ports, through which I could see the magnets and motor windings, and I had thought, “That seems like a potential point of failure, doesn’t it?  Don’t electric motors like to not be contaminated with debris?”  And so I checked those ports consistently.  And I cleared those ports consistently.  And the motors continued to function consistently, even when I was less than perfectly consistent with the cleaning schedule.
It seemed that my suspicion of a fundamental design flaw was unfounded.
Apparently the designers and engineers knew what they were doing.
So I thought.
Until entropy, the ravages of time and the general wear and tear of physical machinery, decided to prove the suspected design flaw was in fact a fundamental design flaw.

So.  
A potential design flaw noted years previously but indifferently dismissed, confirmed in subsequent years as being an actual design flaw but not on the evidence a serious design flaw, proved to be a serious design flaw once combined with general expected physical entropic activity that developed between the previous maintenance event and the latest maintenance event, leading to the near-engulfment of the device.

A fundamental design flaw conspired with my laziness to very nearly set the lawnmower on fire.

I set the lawnmower on fire.