'Don't count your chickens
Before they are hatched.'
Why not?
I like practising my arithmetic
in advance, it never was my best subject

As for kettles not boiling if watched
Should the same rule apply
to saucepans?
should we expect burned pots and raw vegetables
Further, if 'eating an apple a day
Keeps my gorgeous doctor away.'
I will stick with bananas
Yes, I can hear you think
'She's bananas'