"Ken Blake said:
I, too, don't usually point out obvious typos - as you say, one can
easily be hoised by one's own petard; however, it is an accepted
convention that typos in pedantry must be seized upon (-:. [And also
that the seizing itself will then be found to have one or more errors in
it. (Hoised isn't one.)]
It isn't? As far as I know, the correct quotation is "hoist..."
OK, here goes ... I'm glad someone took the bait!
The expression is usually used these days to mean caught out by your own
trap.
The original means blown up by your own bomb: a petard is a small bomb
or grenade, as might be used by an assassin or terrorist. (Originally a
French word, I think.) If he didn't throw it hard/far enough, or
sheltered behind an insufficiently strong wall or whatever, it would get
him too.
Granted, "hoised" is probably obsolete too, and I'm sure by simple
(mis)usage, the expression _is_ shown in most dictionaries nowadays as
hoist. But to me hoist (which in normal modern English would be hoisted
anyway, I think) suggests being lifted, usually by a rope or similar -
which is not the same as being blown up.