EXPLANATION Say the rows of words below from left to right. Listen to the sound and you will realise that the first two words have a short vowel sound (as in hop) but that the last two have a long vowel sound (as in hope), caused by the e at the end of the word. (Note that all these words have only one syllable: that is, they are monosyllabic.)
mop - mopping
cop - copping
lop - lopping
mat - matting
tap - tapping
can - canning
mope - moping
cope - coping
lope - loping
mate - mating
tape - taping
cane - caning
From the list above, you will realise that before we add the suffixes -ing or -ed to words like hop (which does not end with an e), we double the final consonant (p), giving hopping or hopped. (The effect is to keep the vowel sound short.)
On the other hand, when adding -ing or -ed to words that end in an e, such as hope, we simply take off the e and add the suffix, giving hoping or hoped. (The effect is to keep the vowel sound long.)