Opportunity knocks. But it really doesn't. It's actually a Conductor there to say there's a Train for you at the metaphorical Train Station, ready to take you to a greater destination. All that's left for you to do is get to the station and climb aboard.
Well, Opportunity didn't knock. I saw the Conductor coming and raced to the Train Station to await the longed for "All aboard!"
I sat on the platform admiring the Train. But I wasn't called aboard; it was desolate of a crew.
I picked my fingernails and gave the Train anxious glances. But I wasn't called aboard.
I began securing all the cars for their departure: checking that they were each properly latched to the other, and then in turn to the Engine.
I began gathering wood to feed the fire.
But I wasn't called aboard.
I opened the furnace, to check its heat. I stoked the fire. I added more wood. I adjusted the coals. I let more air in and still more wood and still more air and I stoked it till my brow bled sweat and all it amounted to was the explosion of the Engine. I did not ensure the Train would leave with me as a giddy passenger. I ensure that the Train would never leave, regardless of my being on board. I left the Train desolate, to be dragged away and recycled for other Opportunity Trains of people strong enough to wait.
And who's to say, in but a moment's time, the Conductor would have tipped me his hat. Who's to say he'd have bellow "All aboard!" and taken my hand as I mounted the steps.
Who's to say the Train was truly going to leave, but my exuberant human nature brought me to forcing Fate and destroying that destination. And perhaps the Train would have taken me somewhere only to shortly pick me up and return me to my original standing, the only difference being my minutely wiser outlook toward similar situations. Or perhaps that Train was one of two much larger Trains, and the passage on either affects life's outcome immensely. Perhaps I destroyed the better option.
Or perhaps the Engine isn't in fiery ruin.
Perhaps it just needs a little more wood.