Why does Excel SUMIF function return #ERROR

Question

Learning SUMIF right now on excel. Why does this line work in a cell:

 =SUMIF(A:A,"<1/3/2020" ,F2:F102)

But this one gives me "#ERROR!" where cell O2 is the date 1/3/2020

 =SUMIF(A:A, <O2 ,F2:F102)

Answer 1

Change <O2 to "<" & O2

=SUMIF(A:A, "<" & O2 ,F2:F102)