Why does Shomer Ru'ach not seed?
Rashi: He waits until wind comes (Rashbam - it is good to seed when there is wind 1 ), and sometimes it does not come. Rashbam - therefore, he does not seed much. Rid - sometimes the time for seeding passes, and he cannot seed after this.
Ibn Ezra: Also this is a Mashal for a Nadiv (generous person). A lazy, stingy person who seeds, he says 'the wind shows that rain will not fall in the coming days. Why should I take my seeds and bury them in the ground?'
Seforno: He fears lest a storm wind scatter seeds. Even though this is possible, he should not refrain due to this fear. If so, he will never seed!
Metzudas David: The wind scatters the seeds everywhere.
Why does Ro'eh ve'Avim not harvest?
Rashi: He looks at the clouds, and when he sees them darkening, he fears to harvest due to [impending] rain. He never harvests, for he always fears. Rashbam - every morning he surely sees clouds 1 . Rather, one should not be lazy due to morning clouds; he should harvest when possible. If he refrains today, perhaps the rain will not come today, rather, tomorrow. Every day he will be idle from harvesting!
Rid: Sometimes the summer passes, and the days of rain come, and he cannot harvest now!
Are there not mornings without clouds?! (PF)