Typescript does not recognize that iterator can index class when using forEach to loop over members of class [duplicate]

I am trying to iterate over the keys of a class using the forEach function

const foo = {
  a: 'hello',
  b: 'world',
}

Object.keys(foo).forEach(k => console.log(foo[k]))

However I get the error:

Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{ a: string; b: string; }'.
  No index signature with a parameter of type 'string' was found on type '{ a: string; b: string; }'.ts(7053)

Using a suggestion I found on a different post I was able to fix this with

Object.keys(foo).forEach(k => console.log(foo[k as keyof typeof foo]))

However I don't understand why this is necessary? Is there no way for typesript to know that k will always be a key of foo?