I can't grow lily of the valley and I love them.
I've tried buying the pips, transplanting them from a friend (with permission) and buying young plants but they always produce a couple of feeble shoots and then die.
I follow all the instructions and plant them in suitable conditions.
Being an optomist I shall try again this year.
I used to be unable to grow lobelia from seed but kept trying and last year ended up with so many plants I had to give them away.