You & I nothing without each-other

How can you “SM_LE” without ‘I’?
How can you be “F_NE” without ‘I’?
How can you “W_SH” without ‘I’?
How can you be “FR_END” without ‘I’?
“I” am very important!
But this “I” can never achieve “S_CCESS” without “U”!