Isaiah 58:5 "Is it a fast like this which I choose,  a day for a man to humble himself?  Is it for bowing one's head like a reed, And for spreading out sackcloth and ashes as a bed?  Will you call this a fast, even an acceptable day to the LORD?”

A convenient fast is what fits your schedule.

Which ever way the wind is blowing at the time, determines the way you bow down and fast.  Maybe you lost your job, or the church is facing some challenges.  There’s a storm wind, so you react and fast.

You fast with an altered appearance and attitude. If your motive is to be seen, then you are seen.

Prayer coaching.  “Jesus,  Help me to fast the way you choose.  Inspire me not to fast only when it’s convenient for me.  ”