I have been trying hard to understand the concept of sampling some contexts. The main thing is I am unable to digest the idea of sampling. For example in Mikolov's papers, the negative sampling expectation is formulated as : logσ(⟨w,c⟩)+k⋅𝔼cN∼PD[logσ(−⟨w,cN⟩)] I clearly understand the left term logσ(⟨w,c⟩), but I can't understand the very idea of sampling negative word-context pairs.

I have been trying hard to understand the concept of negative sampling in the context of word2vec. I am unable to digest the idea of [negative] sampling. For example in Mikolov's papers the negative sampling expectation is formulated as

$$\log \sigma(\langle w,c\rangle ) + k \cdot \mathbb E_{c_N\sim PD}[\log\sigma(−\langle w,c_N\rangle)].$$

I understand the left term $\log \sigma(\langle w,c\rangle)$, but I can't understand the idea of sampling negative word-context pairs.