As others have noted, people are assuming 5e's CR system works the same as 3e's (which since they are exactly the same name, I can understand).
3e's system attempted to combine both the single challenge of a monster as well as the number of monsters to a single value. This system ultimately didn't work that well.
5e's system divides challenge into two different components.
1) CR: As someone else mentioned, this is the "too tall to ride" indicator. All CR is meant to do is warn you that certain monsters are too good for your party. If you have a Level 3 party, and they face a CR 5 monster...there is high likelihood that someone in the party is going to die. It is not meant to indicate the total challenge to your party.
2) XP budget: This is where the "real challenge building" work actually occurs. You take the XP values of the various monsters you want to use on your party, get a final number, and compare it to the XP budget for your party. Assuming you have chosen proper CR monsters (aka CR = party level or lower), then the XP budget determines the final challenge to your party.
3e's system attempted to combine both the single challenge of a monster as well as the number of monsters to a single value. This system ultimately didn't work that well.
5e's system divides challenge into two different components.
1) CR: As someone else mentioned, this is the "too tall to ride" indicator. All CR is meant to do is warn you that certain monsters are too good for your party. If you have a Level 3 party, and they face a CR 5 monster...there is high likelihood that someone in the party is going to die. It is not meant to indicate the total challenge to your party.
2) XP budget: This is where the "real challenge building" work actually occurs. You take the XP values of the various monsters you want to use on your party, get a final number, and compare it to the XP budget for your party. Assuming you have chosen proper CR monsters (aka CR = party level or lower), then the XP budget determines the final challenge to your party.
