Theory:
The consonant pair TH can have two similar but different sounds in English, and they are both often confused with the sound of the consonant D.
Day
They
Think
all sound differently.
Words that sound like Day are DOG, DRINK, and DO.
Words that sound like THEY are THIS, THAT, and THEN.
Words that sound like THINK are THROW, PATH, and MOUTH.
The consonant pair CH can have three sounds:
K as in CHRISTMAS,
CH as in CHURCH,
CH as in MACHINE, which is a SH sound.
With many words, when the CH comes in the middle of the word, it is pronounced like SH:
PARACHUTE, BROCHURE, MACHINE.
But this is not a fixed rule.