Some of the complexity is the ‘rules’ of the English language, that all have exceptions, and these homophones

Homophones

Homophones are words that sound the same but are spelt differently, and have different meanings.

There, Their and They’re.

One of the most common ones which tend to confuse people

Their means belonging to, or part of them.

• They sold their car. (The car belongs to them)
• The comments hurt their feelings (Feelings that are part of them)

There has two uses: it shows place and it is used with the verb ‘to be’. An easy way to remember it is, here, there and everywhere are place words.

• The bus was parked there. (Position of the bus, showing place.)
• I am going there tomorrow. (To that place)
  

• There have been many accidents on that roundabout. (Have been is a form of the verb ‘to be’.)
• Is there a doctor on duty?
  (Is comes from the verb ‘to be’)

They’re is a shortened form of ‘they are’ and the easiest to remember, as it can be replaced with ‘they are’.

• They’re often out at this time of day. (They are often out at this time of day.
• Do you know where they’re going? (Do you know where they are going?)

Weather and Whether

Weather refers to talk about sunshine, wind, rain, fog etc.

• The weather is cold for this time of year.
• The weather forcast said it would rain.

Whether can be replaced with if in some sentences.

• I'm not sure whether she'll be there or not.
• Do you know whether it is male or female?

Stationary and Stationery

Stationary means standing still or not moving.

• The traffic on the motorway was stationary.
• The queue at the Post Office was stationary

Stationery refers to notepaper, writing paper, envelopes etc. Can easily remember this by 'e' for envelopes.

• We need to order some more office stationery
• You'll find the paper in the stationery cupboard.