so simple(,) yet so inspiring / The next time (that/when) you fail and feel battered...
1.
a. The words are so simple, yet so inspiring.
b. The words are so simple yet so inspiring.
c.The message is simple, yet inspiring.
d.The message is simple yet inspiring.
→Are they all correct? Should I add a comma before "yet"? Which one do you prefer, with or without the comma?
2.
a. The next time you fail and feel battered and bruised by an experience, remember that Japanese proverb and just give it another go.
b. The next time *when* you fail and feel battered and bruised by an experience, remember that Japanese proverb and just give it another go.
c. The next time *that* you fail and feel battered and bruised by an experience, remember that Japanese proverb and just give it another go.
→Are they all correct? Which one is more common?
Thanks!