Valmiki Ramayana Ayodhya Kanda Sarga 28 Shloka 17

मैथिलि O daughter of Mithila, वनचरैः by wanderers in the forest, यताहारैः with limited food, यथालब्धेन whatever is available, तेन with that alone, सन्तोषः satisfaction, कर्तव्यः should be derived, अतः for that reason, वनम् forest life, दुःखम् is difficult.

The wanderers in the jungle, O daughter of Mithila, have to be satisfied daily with whatever little food is available. So forest (life) is a hard life.