I don't even know why it is that I have to say this but I recently ran into some people in Mexico that were turned away from an island nation that will remain unnamed when they turned up there without a visa. Because they are from a G8 country, they just presumed that they would be given a visa on arrival. Now I will admit that often this is the case if you are from one of the more "powerful" countries in the world and a lot of Americans (these people were not American, they were German) think that they are for some reason entitled to visas on arrival without preparing for it ahead of time.
Their excuse was also that it was for some reason the job of the airline to let them know that they need a visa before they get on the plane. In my mind this is just very poor planning on their part and I have zero sympathy for the fact that they were forced to buy a ticket out of there and were not even allowed out of the international terminal.
I really don't think that it is a lot to ask of someone to get on the internet for just a few minutes and find out if the country they are traveling do requires a visa or not. Now in the case of certain countries, there might not actually be a consulate for whatever country that you intend to go to next and yes, this can problematic if said country doesn't have some sort of online visa processing service. The thing is though, that these days almost all countries have some form of online visa service without necessitating going into a physical building and applying in person.
There is a certain amount of arrogance that comes along with being from a particular nation but something that everyone, including Americans, need to be aware of is that just because your country is economically and perhaps militarily powerful, doesn't necessarily mean that every country is just going to let you walk in without a visa. Most of them will, I will admit that, but these days there is a certain level of entitlement that comes along with some people from certain countries and you really shouldn't be that way.
If you are American I have a helpful website for you if you want to know if you need a visa to any country in the world. It is called CIBT Visas and you can investigate very quickly whether or not you need a visa for every single country in the world. I have been using this website for years and they keep their information up-to-date. Now of course you should always double check with the website of that particular country as well but this is a good place to start. If you are not from the USA I am sure there is something similar in regards to your own nationality but since I am American, this is the only one that I ever look at. Sorry.
One of the worst things that can happen during your laid-back travels around the world is to be a little too laid back because it has been my experience all over the world and including in my own country that Immigration officials at the airport tend to be the most humorless, robotic, and un-empathetic workers that the nation in question could possibly find. They do not care if you "didn't know" and there is nothing they can or will do for you at this point.
Do yourself a favor and prepare beforehand when you are going from one country to the next because especially if you are traveling long-term on a limited budget, being forced to buy a last-minute ticket out of the country that you just arrived in can put a huge dent in your finances very quickly. People are unlikely to make this mistake twice but in my mind it is just better to not make the mistake at all in the first place. Once again, if you are American you can check whether or not you need a pre-arranged visa for every country in the world at this website and there are many others out there that function exactly the same way.
I just vouch for this one because I have been using it for years and it has never been incorrect.