Why it sucks to be a landlocked country

The easiest and cheapest way to trade is through the ocean. Without a coastline, a nation cannot trade directly with the ocean. A significant amount of the world's trade is conducted through ships, so oceanic access is ideal. Trade is also possible through (some) rivers and lakes, and some landlocked nations have access to major rivers and lakes, but you still rely on your neighbours for access to the ocean, so that ships can enter the rivers and lakes. This means that you require both friendly relationships with your neighbours and you also hope that they have good infrastructure. Even if trading with a nation who shares your continent, you still rely on your neighbours to be able to trade with them. The below is a pretend map of a pretend continent. The continent is surrounded by the ocean and has a giant lake in the middle of it.

If country A wishes to trade with country D, then they have two options. Trains and trucks can travel through Country B or Country C, or a ship can travel through the ocean and bypass both countries. If country A wanted to trade with another country in a different continent, then a ship can travel from country A to that continent. However, if Country C wants to trade with Country I, they need access to country A's roads and railways. If Country A is underdeveloped and/or refuses to grant them access, then it becomes significantly more difficult to trade with Country I. Assuming that Country A has excellent relations with Country C, and that Country A has excellent infrastructure, then Country C could easily trade with Country I through Country A. However, it will be less economical to do so. Trucks and trains require roads and railway lines, which cost money to maintain, water does not have maintenance fees.  Also, trucks require a driver per vehicle, which has a limited capacity. 

Let's look at another situation now. If Country G wishes to trade with Country F, then the lake is a suitable trading route. However, if Country F wishes to trade with Country B, with the use of ships, then the ship needs to travel from the lake through the river to Country B. Since the river is completely within Country G, Country H and Country J, and it is completely their territorial waters, Countries F and B rely on G, H and J to trade. If country F wishes to trade with a country on a different continent, then they either need to send trains and trucks through to the closest port in Country I, or send ships through the river. If country H wishes to trade with either of the lake countries, then ships have to pass through Country D, and if Country H wishes to trade with other continents, they rely on Country J. If Country H decides to block the river to all trading ships, then that means that Countries F, E and G can only trade with each other, if using ships. Country D is in the fortunate position of having a coastline on the lake and on the ocean, meaning that they can trade with ships on both waterways. It is also significantly more difficult for a land-locked country to have a navy. This usually means that landlocked countries are both neutral and poor, though there are exceptions. This is why landlocked countries outside of Europe are amongst poorest nations in the world, This is why landlocked countries are neutral in their alliances There might be other factors which contribute to both, however, being landlocked is a big factor. Having a coastline, however, is not enough. In order to be able to send ships through, there needs to be warm water (i.e. it doesn't freeze in winter) and the water needs to be deep-enough. For trade to be successful, both criteria must be met in the same place.  If you have warm water ports which are shallow, or deep water ports which freeze, then you might as well be landlocked. Ice breakers do exist, but they are extremely costly, and in some cases, the ice can freeze again before the ship can pass through the cleared path.