You notice the warmth of the sun more when it's cold.
You realize the importance of something when you lose it.
You only appreciate your job once you lost it.
You notice the warmth of the sun more when it's cold. = 寒い時により太陽の暖かさに気づく
Notice, realize = 気づく
You realize the importance of something (for the first time) when you lose it. = 何かを失って(初めて)その大切さに気づく。
for the first time = 初めて
You only appreciate your job once you lost it. =仕事を失ってから仕事にありがたみを感じる。
appreciate = 〜に対して感謝の気持ちを持つ、ありがたみを感じる
どうぞご参考に。