You can never be a hundred percent sure you’ve caught Laylat al-Qadr on a particular night, and so you should work hard on all the last ten nights. Also, the last ten nights of Ramadan are special by themselves, because the Prophet (PBUH) used to increase his worship during these nights.
Aisha (ra) narrates: “Allah’s Messenger (ﷺ) used to practice I`tikaf in the last ten nights of Ramadan and used to say, “Look for the Night of Qadr in the last ten nights of the month of Ramadan.” (Bukhari 2020)
Also: “With the start of the last ten days of Ramadan, Messenger of Allah (ﷺ) would pray all the night, and would keep his family awake for the prayers. He tied his lower garment and devoted himself entirely to prayer and supplication.” (Al-Bukhari and Muslim, Qt in Riyad al-Salihin B1 #99)
Ibn Umar (Allah be pleased with them) reported Allah’s Messenger (ﷺ) as saying:
“Seek it in the last (ten nights). If one among you shows slackness and weakness (in the earlier part of Ramadan), it should not be allowed to prevail upon him in the last week.” (Muslim 1165 e)
