Since things got a little heated in here, I read everything again from @Doctor_MG and @JackHandy and I don't think Jack was being insensitive only because he was responding to the following statement as written:
"A lot of times the thing that is needed isn't obvious or even possible. Most people don't get mad when the solution can be found (e.g. food, being held, etc). But when a child has been crying for three hours and you've tried seemingly everything...well I understand the frustration."
To me those bolded and underline words, implies you were trying to settle a child using the normal things because you thought it was one of the things the baby needs. Once you have exhausted those things, it then implies there is something wrong with the child that you are NOT aware of. Those original words do not consider an underlying condition, and are then brought into the replies later as a case scenario.
Therefore, under that scenario of unknown what is wrong with your child, if they are crying for so long then google as Jack said is right, take them to get treated. There is no implication that you are a bad parent if your child has underlying conditions that you know about and you know that no matter what you do sometimes won't stop them for crying. The implication is if you don't know what is wrong with your child and you do nothing then you are a bad parent and I would agree with that.
So the point I am trying to make is that English can be a complex language in interpreting it, especially in written form, as my explanation is how I interpret those words and I am sure others were different. English is also not everyone's native tongue, so rather then both people get defensive, we should try to think a bit why heads are clashing, and usually in scenarios like this is because there is a bit of misaligned communication.
