Engine cranks but won't start up

Yeah did that first, did need to get a new battery but after installing that, still would crank but not turn over. So started searching on line and came across this forum and read what several had already tried to do or had to do while wanting to throw up thinking of the gobs of money I'd have to spend to "fix". Then came across people talking about fuses and tadaaa, pulling #43 for whatever reason ....worked! But is mind boggling why that particular fuse as it was for "backup light relay" SMH! Just happy I didn't have to spend but $150 on the new battery as many others on here spent a TON and hope what they spent, was TRULY the cause of their issues.